Mobilization of the Escherichia coli plasmid ColE1 (colicin E1) and ColE1 vectors used in recombinant DNA experiments.

The Escherichia coli Co1E1 plasmid, which codes for production of colicin E1, is inherently nontransferable (nonconjugative) by bacterial mating. Co1E1 can be transmitted at mating by a process called mobilization if Co1E1 is coresident with a transfer plasmid. Mobilization is governed in part by a Co1E1 gene called mob. Co1E1 is mob+. Several Co1E1 derivatives employed in recombinant DNA experiments, notably pBR313 and pBR322, are mob-. These cloning vehicles are mobilized at markedly reduced frequency relative to Co1E1. E. coli K12 carrying either pBR313 or pBR322 represents a useful host vector system for recombinant DNA experiments and affords a significant degree of biological containment.